Buggy code:
public class DecafParser extends LLkParser implements DecafParserTokenTypes { private boolean error ; @ Override public void reportError ( RecognitionException ex ) { } @ Override public void reportError ( String s ) { } public boolean getError ( ) { } public void outputError ( ) { } private boolean trace = false ; public void setTrace ( boolean shouldTrace ) { } @ Override public void traceIn ( String rname ) throws TokenStreamException { } @ Override public void traceOut ( String rname ) throws TokenStreamException { } protected DecafParser ( TokenBuffer tokenBuf , int k ) { } public DecafParser ( TokenBuffer tokenBuf ) { } protected DecafParser ( TokenStream lexer , int k ) { } public DecafParser ( TokenStream lexer ) { } public DecafParser ( ParserSharedInputState state ) { } public final void program ( ) throws RecognitionException , TokenStreamException { } public final void field_dec ( ) throws RecognitionException , TokenStreamException { } public final void method_dec ( ) throws RecognitionException , TokenStreamException { } public final void type ( ) throws RecognitionException , TokenStreamException { } public final void array_dec ( ) throws RecognitionException , TokenStreamException { } public final void block ( ) throws RecognitionException , TokenStreamException { } public final void var_decl ( ) throws RecognitionException , TokenStreamException { } public final void statement ( ) throws RecognitionException , TokenStreamException { } public final void line ( ) throws RecognitionException , TokenStreamException { } public final void assignment ( ) throws RecognitionException , TokenStreamException { } public final void method_call ( ) throws RecognitionException , TokenStreamException { } public final void if_statement ( ) throws RecognitionException , TokenStreamException { } public final void for_statement ( ) throws RecognitionException , TokenStreamException { traceIn ( "for_statement" ) ; try { returnAST = null ; ASTPair currentAST = new ASTPair ( ) ; AST for_statement_AST = null ; try { AST tmp52_AST = null ; tmp52_AST = astFactory . create ( LT ( 1 ) ) ; astFactory . makeASTRoot ( currentAST , tmp52_AST ) ; match ( TK_for ) ; match ( LPAREN ) ; AST tmp54_AST = null ; tmp54_AST = astFactory . create ( LT ( 1 ) ) ; astFactory . addASTChild ( currentAST , tmp54_AST ) ; match ( ID ) ; AST tmp55_AST = null ; tmp55_AST = astFactory . create ( LT ( 1 ) ) ; astFactory . addASTChild ( currentAST , tmp55_AST ) ; match ( ASSIGN ) ; expr ( ) ; astFactory . addASTChild ( currentAST , returnAST ) ; <START_BUG> match ( COMMA ) ; <END_BUG> expr ( ) ; astFactory . addASTChild ( currentAST , returnAST ) ; match ( RPAREN ) ; block ( ) ; astFactory . addASTChild ( currentAST , returnAST ) ; for_statement_AST = ( ( AST ) ( currentAST . root ) ) ; } catch ( RecognitionException ex ) { reportError ( ex ) ; recover ( ex , DecafParser . _tokenSet_5 ) ; } returnAST = for_statement_AST ; } finally { traceOut ( "for_statement" ) ; } } public final void expr ( ) throws RecognitionException , TokenStreamException { } public final void location ( ) throws RecognitionException , TokenStreamException { } public final void assign_op ( ) throws RecognitionException , TokenStreamException { } public final void method_name ( ) throws RecognitionException , TokenStreamException { } public final void callout_arg ( ) throws RecognitionException , TokenStreamException { } public final void expr_l0 ( ) throws RecognitionException , TokenStreamException { } public final void or_op ( ) throws RecognitionException , TokenStreamException { } public final void expr_l1 ( ) throws RecognitionException , TokenStreamException { } public final void and_op ( ) throws RecognitionException , TokenStreamException { } public final void expr_l2 ( ) throws RecognitionException , TokenStreamException { } public final void eq_op ( ) throws RecognitionException , TokenStreamException { } public final void expr_l3 ( ) throws RecognitionException , TokenStreamException { } public final void rel_op ( ) throws RecognitionException , TokenStreamException { } public final void expr_l4 ( ) throws RecognitionException , TokenStreamException { } public final void linear_op ( ) throws RecognitionException , TokenStreamException { } public final void expr_t ( ) throws RecognitionException , TokenStreamException { } public final void mul_op ( ) throws RecognitionException , TokenStreamException { } public final void logical_not ( ) throws RecognitionException , TokenStreamException { } public final void expr_tm ( ) throws RecognitionException , TokenStreamException { } public final void unary_minus ( ) throws RecognitionException , TokenStreamException { } public final void expr_tf ( ) throws RecognitionException , TokenStreamException { } public final void literal ( ) throws RecognitionException , TokenStreamException { } public static final String [ ] _tokenNames = new String [ ] { "<0>" , "EOF" , "<2>" , "NULL_TREE_LOOKAHEAD" , "\"true\"" , "\"false\"" , "\"boolean\"" , "\"break\"" , "\"callout\"" , "\"class\"" , "\"continue\"" , "\"else\"" , "\"for\"" , "\"if\"" , "\"int\"" , "\"return\"" , "\"void\"" , "\"while\"" , "\"Program\"" , "{" , "}" , "LSQUARE" , "RSQUARE" , "LPAREN" , "RPAREN" , "WS_" , "SL_COMMENT" , "ML_COMMENT" , "NOT" , "MINUS" , "MUL" , "DIV" , "MOD" , "PLUS" , "LT" , "GT" , "LEQ" , "GEQ" , "EQ" , "NEQ" , "AND" , "OR" , "ASSIGN" , "INC_ASSIGN" , "DEC_ASSIGN" , "COMMA" , "SEMI" , "ID" , "INTLITERAL" , "DEC_LITERAL" , "HEX_LITERAL" , "BIN_LITERAL" , "ALPHA_NUM" , "ALPHA" , "DIGIT" , "HEX_DIGIT" , "BIN_DIGIT" , "CHAR" , "STRING" , "ESC" , "CHARLIT" , "BLOCK" , "BLOCK_LINE" , "VAR_DECL" , "METHOD" , "FIELD" , "ARRAY" , "MINUS_ASSIGN" , "BOOLEANLITERAL" } ; protected void buildTokenTypeASTClassMap ( ) { } private static final long [ ] mk_tokenSet_0 ( ) { } public static final BitSet _tokenSet_0 = new BitSet ( DecafParser . mk_tokenSet_0 ( ) ) ; private static final long [ ] mk_tokenSet_1 ( ) { } public static final BitSet _tokenSet_1 = new BitSet ( DecafParser . mk_tokenSet_1 ( ) ) ;

Fix:
match ( SEMI ) ;